In car bodywork assembly lines, subassemblies (such as the subframe, the sides of the body, the rear skirt, . . . ) are positioned relative to one another and relative to welding robots. By their very nature, bodywork parts are deformable on being subjected to stresses, so the tooling used for making bodywork of determined and reproducible shape performs two functions: firstly it constitutes framework for each deformable subassembly for the purpose of stiffening it to enable it to be handled by the handling robots, and secondly it constitutes a stable interface enabling positioning to be precise in a fixed frame of reference associated with the welding robots.
Such tools are generally constituted by a structure for holding a bodywork part, which structure comprises members assembled to one another together with auxiliary elements secured to the members for the purposes, for example, of positioning the part in the structure, of holding the part in the structure, of positioning the structure relative to another structure, of making a connection with the handling robot, . . . .
These members are formed by beams made from metal bars of lengths that are determined as a function of the dimensions of the part to be held. With the bars used, it is difficult to have beams that are sufficiently rigid and lightweight for this purpose.
The beams are usually assembled to one another and to the auxiliary elements by welding. This means that they are relatively time-consuming and difficult to make, given the deformations caused by welding, and their fabrication also requires specialized personnel. Furthermore, repairs and additions of auxiliary elements need to be performed by the specialized personnel and with very great care so as to avoid spoiling the shape of the structure. In order to limit deformation, it is common practice to make use of beams and of auxiliary elements of considerable thickness, to the detriment of lightness.
It is also possible to make an assembly by bolting. However it is difficult to position the various beams and auxiliary elements relative to one another prior to assembling them together. An assembly made in this way is generally not sufficiently rigid. Furthermore the beams must be of relatively great thickness in order to allow fixing screws to penetrate sufficiently, and as a result the beams are relatively heavy.
However, tool weight is an important parameter governing the dimensions of the robots that are to handle the tools, and having an influence on the cost of such robots.